This project is designed to investigate the spatial distribution and functional properties of cortical neuron "colonies" in the primate motor cortex and supplementary motor area (SMA) that project to the spinal cord and are associated with individual muscles or closely related groups of muscles, as well as the activity of neurons in such colonies during defined voluntary motor behaviors. Multicontact passive semiconductor electrodes have been successfully implanted in the arm area of the SMA of a primate that was trained to do a number of different wrist movement tasks. Cells seem to be better correlated with complex tasks than simple repetitive tasks. Recorded activity diminishes in amplitude after several weeks but can be restored with microstimulation through the electrode.